(1) Field of the Invention
The invention relates to a method of metallization in the fabrication of integrated circuits, and more particularly, to a method of tungsten metallization which can remove or prevent precipitates after tungsten etchback in the manufacture of integrated circuits.
(2) Description of the Prior Art
A common tungsten plug process is to blanket deposit a tungsten film on a titanium nitride glue layer. The tungsten is etched back with an etch stop at the glue layer. Precipitates are easily formed on the surface of the titanium nitride after tungsten etchback. These precipitates will cause metal hillocks or metal roughness and degrade the reliability of the completed integrated circuit.
In their article, "Improving EM Lifetime of AlCu/TiN Lines and W-Plugs Metal System by Controlling Crystal Structure of AlCu," by H. Horikoshi and T. Nogami, Proceedings of the VMIC Conference, Jun. 8-9, 1993, pp. 244-250, the authors use SF6 and Ar gases to etch back tungsten. This results in the existence of fluorine and sulfur precipitates on the surface of the TiN layer and a roughened TiN surface. They used ammonium hydrogen peroxide to remove the impurities. Alternatively, they used an Argon ion sputtering treatment to remove the damaged portion of the TiN layer. The authors state that they believe the inferior Al alignment is caused not by the roughened surface, but by the existence of the precipitates. No mention is made of preventing future formation of precipitates on the TiN surface after the initial precipitates are removed.